This invention relates to hash-based beam alignment in a phased antenna array, and in particular relates to beam alignment without requiring exhaustive scanning of beam directions.
There is much interest in integrating millimeter wave radios (mmWave) into wireless LANs and 5G cellular networks to benefit from their multiple GHz of available spectrum. Yet unlike existing technologies, e.g., WiFi, mmWave radios require highly directional antennas. Since the antennas have pencil-beams, the transmitter and receiver need to align their antenna beams before they can communicate. Existing solutions scan the entire space to find the best alignment. Such a process has been shown to introduce up to seconds of delay, and is unsuitable for wireless networks where an access point has to quickly switch between users and accommodate mobile clients.
The IEEE 802.11ad includes a beam searching mechanism, however, is not defined in detail in the standard documentation, and it has been left open to the manufacturer. This has resulted in several variations of the 802.11ad beam searching mechanism presented in different documents. However, at a high level, it works in three stages in order to find the best beam alignment between an access point (AP) and a client [3, 8].
The first stage is called Sector Level Sweep (SLS). In this stage, the AP transmits in all possible directions, and the client sets its receiver beam pattern to a quasi-omnidirectional beam. The process is then repeated with the AP setting its receiver antenna to quasi-omnidirectional and the client sweeping through all transmit directions. At the end of this stage, the AP and client each pick the γ directions that deliver the largest power. The second stage is called Multiple sector ID Detection (MID). This stage repeats the process above but with the transmit beam set to quasi-omni-directional and the scan being performed with the receive beam. This stage compensates for imperfections in the quasi omnidirectional beams. The third stage is called Beam Combining (BC). In this stage, each of the γ best directions at the AP are tried with each of the γ directions at the client. Hence, γ2 combinations are tested and the combination of transmit and receive beam directions that deliver the maximum power is then selected and used for beamforming during the data transmission.